1. Field of the Invention
This invention relates to a process of making artificial teeth.
2. Description of the Prior Art
In the previously conventional process of making artificial teeth, the clinical conditions in the mouth of the patient are reproduced in that impressions are taken and are used to make patterns. A process of making artificial teeth must ensure that the artificial teeth which are made will exactly fit because such exact fit is required for a safe anchoring and a permanent retention of the artificial teeth or the dentures comprising such teeth so that all tissues which are involved in the chewing operation will be able to take up the physiological loads without suffering damage.
All operations performed by the dentist and all operations which are subsequently performed by the dental technician in the making of artificial teeth are performed by methods which have been used for decades and will now briefly be described with reference to the provision of an individual crown:
(1) An impression from the tooth stump which has been prepared is taken by means of a rubber-elastic or hydrocolloidal impression-taking material;
(2) The tooth stump is temporarily protected;
(3) A superhard gypsum is cast into the impression and a working pattern as well as a counterbite pattern are made;
(4) The patterns are installed in an articulator;
(5) An artificial crown is cast from metal in a mold prepared by means of a wax pattern,
(6) The casting is fitted on the tooth stump in the mouth and the artificial crown is finally fixed.
That conventional making of artificial teeth from metal or other materials requires a large number of operations to be performed by the dentist and the dental technician. Said operations involve a risk of a large number of inaccuracies and errors so that an exact fit of the artificial tooth or teeth may not be obtained and the operations may have to be repeated.
These disadvantages may be due to properties of the materials employed, such as the tendency of gypsum to expand and the tendency of metal to shrink, but may also be due to improper work and to difficult conditions in the mouth.
For some time it has been endeavored to replace the conventional taking of an impression and the succeeding operations by other techniques, which depend on the use of mechanical or optical three-dimensional measuring and scanning means. The informations which have thus been obtained are stored and are delivered to control devices of numerically controlled machine tools which have already been introduced for general machining operations.
U.S. Pat. No. 4,182,312 illustrates a mechanical scanning to obtain information on three-dimensional surfaces of teeth and surrounding tissue directly from the patient. For that purpose a probe is moved by the dentist in the patient's mouth. But inaccuracies will always be involved in mechanical scanning.
In the process described in U.S. Pat. No. 3,861,044 a cavity of a tooth is photographically recorded and the dentist shapes a filling body of wax to give it the desired final shape.
In the method described in European Patent 0.054 785, corrections of shape are also required before the fit is as exact as is required. Before such shaping, the three-dimensional and topographic shape of surfaces of organs of the body is optically detected without contacting them.
In the process disclosed in European Patent 0 040 165 it is endeavoured to obtain data of a prepared tooth stump by holographic interferometry and to transmit such data. Light that is generated by a laser is subjected to optoelectronic processing and the resulting data are delivered to a computer. Whereas that process has been described in European Patent 0 040 165, such process has not yet been performed in practice.